Method for the Separation by Distillation of Pure Trioxane

Abstract

The present invention relates to a process for distillatively removing pure trioxane from a feedstream (I) comprising trioxane in a proportion of at least 50% by weight, based on the total weight of the feedstream (I), and additionally formaldehyde and water, which comprises feeding the feedstream I and a further aqueous stream (II) which does not contain any components extraneous to the feedstream to a dividing wall column (TWK 1 ) having a dividing wall TW which is arranged substantially perpendicularly and divides the column interior into a feed region (A 1 ), a withdrawal reaction (B 1 ), an upper combined column region (C 1 ) and a lower combined column region (D 1 ), and drawing off from the first dividing wall column (TWK 1 ) a bottom stream (III) comprising pure trioxane and a sidestream (IV) at the withdrawal region (B 1 ), comprising pure water.

1 - 52 . (canceled)  
   
   
       53 . A process comprising: 
 (a) providing a feedstream and a fit aqueous steam to a first dividing wall column, wherein the feedstream comprises trioxane, formaldehyde and water, the trioxane being present in the feedstream in an amount of at least 50% by weight based on the total weight of the feedstream, wherein the further aqueous stream contains no components extraneous to the feedstream, and wherein the first dividing wall column has a dividing wall arranged within an interior of the column in a longitudinal direction of the column and wherein the dividing wall divides the interior of the column into a feed region, a withdrawal region, an upper combined column region and a lower combined column region;    (b) distilling the feedstream and other aqueous stream within the column to separate the trioxane, water and formaldehyde; and    (ac) removing; (i) from the lower combined column region a bottom stream comprising pure trioxane, and (ii) from the withdrawal region a sidestream comprising pure water.    
   
   
       54 . The process according to  claim 53 , wherein the feedstream comprises 60 to 80% by weight of trioxane, 10 to 30% by weight of water and 3 to 20% by weight of formaldehyde.  
   
   
       55 . The process according to  claim 53 , wherein the first aqueous stream comprises at least 10% by weight of water.  
   
   
       56 . The process according to  claim 53 , wherein the feedstream comprises a trioxane synthesis reactor effluent concentrated to a trioxane content of at least 50% by weight by removing low boilers and high boilers.  
   
   
       57 . The process according to  claim 56 , wherein the feedstream comprises a side draw stream from a second dividing wall column,  
   
   
       58 . The process according to  claim 57 , wherein a bottom stream from the second dividing wall column, comprising high boilers, is recycled into the trioxane synthesis reactor.  
   
   
       59 . The process according to  claim 57 , wherein the second dividing wall column has a top pressure of 0.10 to 5.0 bar absolute.  
   
   
       60 . The process according to  claim 59 , wherein the first dividing wall column has a top pressure of 0.1 to 15.0 bar higher than the top pressure of the second dividing wall column.  
   
   
       61 . The process according to  claim 53 , wherein one or both of the first dividing wall column and the second dividing wall column has a number of theoretical plates of 4 to 90.  
   
   
       62 . The process according to  claim 61 , wherein 1 to 50% of the total number of theoretical plates in one or both of the first dividing wall column and the second dividing wall column are in the upper combined column region, wherein in each case from 1 to 75% of the total number of theoretical plates in one or both of the first dividing wall column and the second dividing wall column are in the feed region and/or the withdrawal region; and wherein 1 to 50% of the total number of theoretical plates in one or both of the first dividing wall column and the second dividing wall column are in the lower combined column region.  
   
   
       63 . The process according to  claim 53 , wherein the feedstream is fed into the feed region of the first dividing wall column at a feed point arranged at a different height in the dividing wall column than a side draw point in the withdrawal region of the first dividing wall column for removal of the sidestream.  
   
   
       64 . The process according to  claim 53 , wherein one or both of the feed region and the withdrawal region of the first dividing wall is at least partially provided with structured or random packings and the dividing wall is designed with heat insulation in regions provided with structured or random packings.  
   
   
       65 . The process according to  claim 53 , wherein during distilling vapors at a lower end of the dividing wall of the first dividing wall column are divided such that the ratio of the vapors in the feed region to vapors in the withdrawal region is 0.5 to 1.5.  
   
   
       66 . The process according to claims  53 , wherein an effluent liquid from the upper combined column region of the first dividing wall column is collected in a collecting chamber disposed within or outside the dividing wall column and is divided and returned to the feed region and the withdrawal region by a fixed setting or control system at an upper end of the dividing wall such that the ratio of the effluent liquid to the feed region to the effluent liquid to the withdrawal region is 0.1 to 1.0.  
   
   
       67 . The process according to  claim 66 , wherein the effluent liquid is conveyed via a pump to the feed region and is introduced under flow control via a static feed head of at least 1 m and wherein the control system is adjusted such that the amount of effluent liquid introduced to the feed region does not fall below 30% of its normal value.  
   
   
       68 . The process according to  claim 53 , wherein the amount of sidestream removed from the withdrawal region is controlled such that the amount feedstream and Her aqueous stream in the withdrawal region does not fall below 30% of its normal value,  
   
   
       69 . The process according to  claim 53 , wherein the first dividing wall column farther comprises sample access at an upper and a lower end of the dividing wall, and wherein the process former comprises taking samples in liquid or gaseous form from the dividing wall column, and analyzing the samples for composition.  
   
   
       70 . The process according to  claim 53 , wherein the division ratio of liquid at an upper end of the dividing wall is adjusted such that the concentration of high-boiling components for which a certain limiting value for the concentration in the side draw should not be exceeded, in the liquid at the upper end of the dividing wall, is from 5 to 75% of the limiting value in the side draw, and that the liquid division at the upper end of the dividing wall is adjusted such that more liquid is passed to the feed region at higher contents of higher-boiling components, and less liquid at lower contents of higher-boiling components,  
   
   
       71 . The process according to  claim 53 , wherein the concentration of low-boiling components for which a certain limiting value in the sidestream should not be exceeded, at a lower end of the dividing wall, is adjusted to from 10 to 99% of the limiting value specified for the sidestream, and heating output of a bottom evaporator is adjusted such that the heating output is increased at a higher content of low-boiling components and the heating output is reduced at a lower content of low-boiling components.  
   
   
       72 . The process according to  claim 53 , wherein a top stream is withdrawn from the dividing wall column under temperature control, wherein a measurement point in the upper combined column region of the dividing wall column which is disposed from 1 to 25 theoretical plates below an upper end of the dividing wall column is used to define a control temperature.  
   
   
       73 . The process according to  claim 53 , wherein the bottom stream is removed under temperature control, wherein a measurement point in the lower combined column region of the dividing wall column which is disposed from 1 to 25 theoretical plates above a lower end of the dividing wall column is used to define a control temperature.  
   
   
       74 . The process according to  claim 53 , wherein the removal of the sidestream from the withdrawal region of the dividing wall column is under level control and a liquid level in a bottom evaporator is used as a control parameter.  
   
   
       75 . The process according to  claim 53 , wherein the first dividing wall column is substituted with a connection of two thermally coupled columns, each of the thermally coupled columns having a dedicated evaporator and a dedicated condenser.  
   
   
       76 . The process according to  claim 75 , wherein the thermally coupled columns are operated at different pressures and only liquids are conveyed in connecting streams between the two thermally coupled columns.  
   
   
       77 . The process according to  claim 75 , wherein a bottom stream from the first of the thermally coupled columns is at lest partly evaporated in an additional evaporator and is subsequently fed to the second of the thermally coupled columns in biphasic form or in the form of a gaseous and of a liquid stream.  
   
   
       78 . The process according to  claim 53 , wherein the feedstream is at least partly pre evaporated and is fed to the first dividing wall column in biphasic form or in the form of a gaseous and of a liquid stream.